1. Field of the Invention
The present invention relates to a magnetic element used for electronic parts such as inductors, noise filters, transformers, and the like and a method of manufacturing the magnetic element.
2. Description of the Related Art
In recent years, regarding electronic equipment and electronic parts, demands for increasing performance, reducing size, improving safety and the like are becoming stronger. Magnetic elements in particular are often used in important application for operating electronic equipment, such as transmitting a signal, rectifying power supply, and the like. Therefore, increasing performance, reducing size, as well as ensuring more safety are demanded.
A large factor of reducing or limiting performance and safety of magnetic elements is temperature variation (also called temperature load) in environment where they are used. For example, when a magnetic element is used under a condition with relatively small temperature load such as a room temperature, a possibility of reducing performance and safety of the magnetic element is small. However, when electronic equipment having the magnetic element is used under a high temperature condition, or when the magnetic element itself is mounted on a power supply circuit or the like involving relatively large current, various characteristics of the magnetic element may often become unstable. In such cases, in the magnetic element, there arises a possibility of causing thermal runaway or malfunction inside a circuit or equipment. Accordingly, in the case where the temperature load is applied to the magnetic element, stability of temperature characteristics is demanded.
Conventionally, there are magnetic elements which have a coil and at least two or more magnetic cores. As such magnetic elements, further, there is a type in which magnetic cores are butted directly with each other. This type of magnetic element is in a state that end faces (bottom faces orthogonal to a magnetic path) of the magnetic cores are in contact with each other. However, when the end faces being butted are observed microscopically, numerous dents and projections resulting from scratching by grinding, baking the surface of magnetic substance, or the like exist on the end faces. Accordingly, the butted end faces are in a state that the end faces are in contact not entirely but partly. Therefore, the magnetic element has a problem such that when it is subjected to temperature load, and then expansion, contraction and the like occur in the magnetic cores, a change occurs in percentage of contact around minute dents and projections, thereby worsening a change due to a temperature in various characteristics (temperature characteristics of various characteristics).
In order to solve the above-described problem, it is effective to flatten the end faces of the magnetic cores as much as possible. Techniques to flatten the end faces include, in addition to accurate cutting, grinding or the like, use of a chemical polishing method or the like. In such cases, the dents and projections on the end faces can be reduced to a height difference of 3 μm in a possible smallest state. However, the above means require high precision in cutting equipment and grinding equipment, and also the time required in a series of processes largely increases. Therefore, in aspects of cost, process time, and the like, it is not easy to adopt these techniques for mass production of the magnetic element. Here, as a technique to solve the above-described problem, for example, one described in Patent document 1 is known.
In a magnetic element described in Japanese Patent Application Laid-open 2004-103658, a gap is formed by means of cutting, grinding, or the like in at least one position among positions in the magnetic core where a magnetic path is formed, and a rare earth magnet, namely, a bond magnet constituted of a mixture of permanent magnet powder and resin is inserted therein. Thus, it attempts to improve temperature characteristics with respect to various characteristics.
However, for the magnetic element disclosed in Patent document 1, processes such as cutting, grinding and the like are required for making the gap in which the bond magnet can be inserted. Moreover, for the magnetic element disclosed in Patent document 1, operations of such processes are needed to be performed on individual parts. Thus, in the magnetic element disclosed in Patent document 1, productivity is quite low. Also, in the magnetic element disclosed in Patent document 1, a permanent magnet is arranged so as to generate magnetic force in the opposite direction of a direction of magnetic flux flowing in a magnetic core such as ferrite or the like. This requires to pay attention to directivity when mounting inductance parts, and moreover, if an input direction of current is reversed, directions of the magnetic flux and the magnetic force become the same, which causes a problem of adversely affecting the temperature characteristics.
The present invention is made in view of the above-described problems, and an object thereof is to provide a magnetic element having stable temperature characteristics and capable of suppressing a change in various characteristics even when a temperature change occurs, and a method of manufacturing the magnetic element.